Recent years have seen the normalization of the transmission and recording of images (image data) including motion pictures and static images due to the increasing use of various types of network such as the Internet, intranet, and LAN in addition to the development of computer and communications technology and television broadcasts.
Generally, image data is characterized in that the amount of data is greater than other types of electronic information regardless of whether the data is in analog format or digital format. Therefore, when transmitting or recording image data, the amount of data to be transmitted or recorded is reduced by performing image compression. As one method of reducing the amount of image data, a method has been provided in which the consecutive frames of an image (single screens of an image) are compared and the amount of change in the image (i.e. the differential data) is extracted. After that, only the amount of change is transmitted or recorded.
However, information (data) is exchanged between organizations and between individuals using various devices. Consequently, a state often arises where a plurality of groups of image data are transmitted simultaneously using common wiring or frequency bands having the same transmission wave from transmission devices for transmitting image data or relay devices for relaying image data.
However, according to the above conventional technology, when image data is transmitted using one wiring network or frequency band having the same transmission wave, if the image format is one in which the amount of data changes with the amount of change in the transmitted image data, then when the amount of data exceeds the value of the maximum amount of data transmittable (maximum transmission volume) in that frequency band, the problem arises that part of the data or necessary image data can not be transmitted. In particular, when a plurality of groups of image data are transmitted using common wiring or frequency band having the same transmission wave, then when the peaks of the data amounts of the plurality of groups of image data coincide, the likelihood of necessary image data not being transmitted increases.
More specifically, for example, when at the same time as the screen of an image in channel A changes and the new data for the whole screen is transmitted, the screen in channel B which is being transmitted in the same frequency band changes in the same way, the amount of data in the two channels at the same instant may exceed the maximum transmission volume for that frequency band. In this case, a portion of the image data being transmitted is unable to be transmitted and the image in one channel or in both channels is disrupted.
In the above conventional technology, it is possible to avoid loss of image data. This can be achieved by limiting in advance the number of groups of image data transmitted at one time based on the value of the maximum amount of data able to be transmitted in the frequency band being used (the maximum transmission volume) and the peak amount of data of each group of image data. However, in this case, the problem arises that the efficiency of use of the one wiring network or frequency band having the same transmission wave deteriorates.
On the other hand, the optimum resolution of the image data differs depending on the maximum resolution of whichever of a plurality of receivers receives the transmitted image data. Moreover, the optimum resolution of the image data differs depending on how the image data is to be output (displayed or printed) even if the image data is received by the same receiver. However, an image data transmission method capable of corresponding in real time to the optimum resolution required by the receiver has not thus far been provided.
Furthermore, in the conventional technology, when image data comprising an image format in which the amount of data changes with the amount of change in the image is recorded on a recording medium in which the recording position changes with time, the problems arise in the same way that necessary image data may not be able to be recorded and the recording efficiency of the recording medium deteriorates.